This application claims the priority of Korean Patent Application No. 2003-2217, filed on Jan. 13, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a track error detection device that generates a track error signal by a DPD (Differential Phase Detector) method, and more particularly, to a track error detection device that removes a phase offset, and a phase offset removing method thereof which can remove an error signal generated due to circuit errors of the device itself.
2. Description of the Related Art
FIG. 1 illustrates a related art optical pickup device. A laser beam outputted from a light source 1 for recording/reproducing an information signal is reflected by a beam splitter 5, and incident to an object lens 7. The laser beam incident to the object lens 7 forms a light spot on a recording surface of a disc 10. The laser beam reflected from the recording surface of the disc 10 is incident to the object lens 7, and is then received in a light receiving element 3 after permeating through the beam splitter 5.
The light receiving element 3 divides the light spot into parts A, B, C and D, and measures the quantity of light. The quantities of light for the parts A, B, C and D of the light receiving element 3 are detected, and a track error signal is detected based on the detected quantities of light for the parts A, B, C and D.
Meanwhile, the laser beam outputted from the light source 1 is incident to a FPD (Front Pickup Device) 9 after permeating through the beam splitter 5. The FPD 9 detects the power of the inputted laser beam, and controls the light source 1 so as to keep the power of the inputted laser beam constant.
FIGS. 2A and 2B illustrate track error signal generation according to the related art DPD method. FIG. 2A shows an example that an image of a pit recorded on the disc 10 is received in the parts A, B, C and D of the light receiving element 3 of the FDP 9. In FIG. 2A, (a2) shows a state that the image of the pit accurately matches the center of the light receiving element 3, and (a1) and (a3) show states that the image of the pit leans to the left and right, respectively, with respect to the center of the light receiving element 3.
FIG. 2B is a waveform diagram explaining the phase offsets of signals as opposed to the quantities of light received in the parts A and B, in which (a1′), (a2′) and (a3′) show the phase offsets corresponding to the those of (a1), (a2) and (a3) of FIG. 2A. Consequently, the DPD method is a method of detecting a track error signal using the phase offsets caused by the quantities of light.
The track error (TE) signal can be expressed by the following equation.TE=k(ΔΦAB+ΔΦCD)  Equation 1
Here, ΔΦAB is the phase offset between A and B, and ΔΦCD is the phase offset between C and D.
FIG. 3 is a block diagram of a related art track error detection device 20 for detecting a track error (TE) signal, and FIGS. 4A to 4E are waveform diagrams of input/output signals of respective constituent elements of the track error detection device of FIG. 3. Hereinafter, a related art process of detecting a track error (TE) signal with reference to the waveforms of the signals corresponding to the quantities of light received in the parts A and B of the light receiving element 3 of the optical pickup device 10 will be explained.
The track error detection device 20 includes equalizers 11, comparators 13, phase detectors 15, adders 17 and a subtracter/low pass filter (SUB/LPF) 19. The equalizers 11 equalize signals A and B, which correspond to the quantities of light received in the parts A and B of the light receiving element 3 of the optical pickup device 10, and output equalized signals A1 and B1 as shown in FIG. 4A.
The comparators 13 quantize the equalized signals A1 and B1 as shown in FIG. 4A, and output signals A2 and B2 of a digital form as shown in FIG. 4B. Then, the phase detectors (PD) 15, as expressed by the equation 1, detect the phase offsets between the parts A and B and between the parts C and D of the light receiving element 3 to detect the track error (TE) signal. That is, the PDs 15 detect the phase offsets with respect to the output signals A2 and B2 of the comparators 13 as shown in FIG. 4B, and output an up signal ABU and a down signal ABD corresponding to the phase offsets as shown in FIG. 4C.
One of the adders 17 adds the up signal ABU, which is the phase offset signal between the signals A2 and B2, to the up signal CDU, which is the phase offset signal between the signals C2 and D2. The other of the adders 17 adds the down signal ABD, which is the phase offset signal between the signals A2 and B2, to the down signal CDD, which is the phase offset signal between the signals C2 and D2. The signals added by the adders 17 are as shown in FIG. 4D, and the SUB/LPF 19 subtracts and low-pass-filters the added signals, and outputs a track error (TE) signal as shown in FIG. 4E.
However, the foregoing related art has various problems and disadvantages. According to the related art track error detection device as described above, however, the phase offsets among the signals A, B, C and D, which correspond to the quantities of light received in the parts A, B, C and D of the light receiving element 3, may occur due to the circuit errors such as optical aberration, non-ideal pit structure, lens shift, channel mismatch.
FIG. 5 is a view illustrating diverse types of phase offsets. In FIG. 5, (a) shows an ideal case that no phase offset occurs, (b) shows a case that the phase offset occurs between the parts A and D (or B and C), (c) shows a case that the phase offset occurs between the parts A and B (or C and D), and (d) shows a case that the phase offset occurs among the parts A, B, C and D.
According to the related art track error detection device as shown in FIG. 3, the phase offsets are detected with respect to the signals that correspond to the quantities of light received in the parts A and B and in the parts C and D, and the detected phase offsets are added together. Accordingly, the phase offset which occurs between the parts A and D (or B and C) due to the circuit error as shown as (b) in FIG. 5 does not cause any problem, but the phase offset which occurs as shown as (c) and (d) in FIG. 5 cannot be removed.
However, this related art has various problems and disadvantages. Consequently, the related art track error detection device cannot remove diverse types of phase offsets occurring due to the circuit errors, and thus it cannot detect the accurate track error (TE) signal.